The food and related industries have long been seeking new and improved products and techniques whereby edible materials such as seasonings, coloring agents, flavorings and nutrients, particularly liquid agents, may be encased, encapsulated or otherwise embedded, dispersed, or contained in protective enveloping media, for subsequent release. The methods which have been used to achieve encapsulation fall in several broad groups. Some processes call for forming solutions or aqueous emulsions of the agent to be encapsulated with an encapsulating medium such as gum acacia or amylodextrins. The aqueous system is then spray dried to form film-engulfed globule-like particles which contain enveloped material. While this procedure has produced encapsulation, the technique calls for high energy input. Moreover, since the final product is invariably a fine powder, the product has somewhat limited utility.
Another technique has been to solubilize a material such as gelatin to provide a solution. A flavor oil, nutrient or other edible agent is then added with suitable agitation to effect emulsification or dispersion and the system is cooled to form a solid gel. Thereafter, the gel is dried, and then ground. This procedure requires special drying apparatus and carefully controlled drying conditions.
Still other methods use sugar melts as protective coatings. Related processes use carbohydrate materials other than gums or amylopectins, for example, starches. The starch must first be gelatinized, a process in which a substantial ratio of water to starch is employed to produce a starch paste. The flavorings or nutrients are then emulsified in the paste, followed normally, by spray drying. The gelatinized starches are viscous, presenting handling and drying problems.
Spray drying has been the most widely employed technique for the encapsulation of products used in the food industry. However, this process has very serious shortcomings. These are indicated in the comments of Balassa in U.S. Pat. No. 3,780,195:
The elevated temperatures used in spray drying operations tend to volatilize all or part of the most volatile components of the active material. This is a particularly serious problem when the active material comprises very volatile materials such as flavoring oils. The elevated temperatures of the spray drying process also tend to degrade any heat sensitive active materials. If the capsule composition is sprayed into air, there is the danger of oxidizing any oxidation prone materials.
It is an important feature of the present invention that it eliminates the above-indicated deficiencies of the spray drying technique. The process facilitates encapsulation, utilizing a relatively simple procedure in which the water concentration is controlled. Hydrophilic polymers such as natural gums, modified starches and proteins are processed to produce a heavy, viscous paste which is subjected to vigorous agitation and shear so that the material to be encapsulated, including essential oils, food flavors, fragrances, agricultural chemicals such as insecticides, or medicinal compounds such as vitamins and drugs may be distributed throughout the viscous, homogeneous encapsulating material which then serves as a protective matrix for the very finely sized particles of the encased agent, constituting the dispersed phase. The viscous paste is then sheeted on a chilled roll, or otherwise formed and partially dried at relatively low temperatures. Finally, the semi-dried product is ground, followed by any additional drying which may be desired.
It is an important discovery of the present invention that there is no need, in achieving encapsulation, completely to solubilize the protein, gum, or modified starch. A solution, in the usual sense, is not required. The encapsulation can be effected mechanically utilizing the encapsulating material in a homogeneous gel or gel-like form.
A related feature of the invention is that a markedly reduced concentration of water is possible, thus effecting material savings in the energy normally required to dispel the moisture from the final product.
Yet another feature of the invention is that the encapsulation may be carried out at relatively low temperatures. For example, in the encapsulation of a compound such as acetaldehyde, a temperature in the range of about 40.degree. F. is used, followed by sheeting and drying. The method of the invention effects conversions of up to about 40% as contrasted with only about 1 to 5% for conventional prior art procedures. Encapsulation of butter flavors containing diacetyl and butyric acid is conducted at temperatures of about 160.degree. F., below the boiling point of diacetyl, so there is essentially 100% conversion. Again, this is in marked contrast with conventional prior art procedures in which there are great losses in the butter flavor elements.
Based upon the teachings of the present invention, it will be appreciated that when encapsulating an essential oil, such as oil of clove, having a much higher boiling point, emulsification can be carried out at still higher temperatures and drying at proportionally higher temperatures.
A very important feature of the process of the present invention is its versatility. The process may be carried out effectively using such diverse materials as proteins, gums and modified starches. The selection of a particular encapsulating material as the protective matrix is dictated by the ultimate contemplated application. For example, if one wishes to utilize the encapsulated product in a cake mix where the level of moisture is high and where it is desired to retain the flavor during the baking process, one could use a matrix derived from a proteinaceous material, which is less soluble than other matrices, so that the flavor element is liberated more slowly, as the hydration of the protein progresses. In products such as cookies there is insufficient moisture to effect hydration of a proteinaceous matrix. Accordingly, a gum or modified starch encapsulating medium is preferred.
A majority of the encapsulated products used in food today are produced through spray drying techniques. Schock U.S. Pat. No. 2,876,160 describes the use of various modified starches as encapsulating films in spray drying procedures. It is significant that Schock teaches that the viscosity of the solution to be used in the process be 50 centipoises or less, the ratio of water to the matrix material being relatively high. In the practice of the present invention it has been found that when using a modified starch such as Capsul (National Starch and Chemical Co.) as the encapsulating material, the desired gel is produced by using 15 parts of water to about 80 parts of the modified starch. In contrast, for spray drying, about 120 parts by weight of water is used to 80 parts by weight of Capsul.
There are many facets of and parameters pertaining to the process and to the raw materials used in practicing the present invention. Relevant to the efficacy of a particular product for a specific use are the encapsulating or encasing medium, the "active" agent to be encased, the water concentration, the temperature and the viscosity of the mixture during the applied shearing stress and mechanical working, the forming or shaping of the paste-like product, the pre-drying, and the final drying and sizing of the ultimate product to provide the desired granulation. All of these variables affect the formulation of the homogeneous matrix, the nature of the completeness of the microdispersion, and the stability of the final product in shelf storage.
The matrix material may, in accordance with the invention, be a protein such as casein, gelatin or wheat gluten. Each is hydrophilic and each reacts in aqueous systems (at variable rates) to form viscous hydratable products. Alternatively, the matrix material may be a gum or modified starch, each characterized in being capable of forming stable, viscous, homogeneous pastes with relatively low concentrations of water, and each receptive to the distribution of the active agent therethrough as a microdispersion.
If the final product is to be incorporated in a chewing gum, a slow release of the active agent is the goal. Accordingly, the use of a protein is dictated, since proteinaceous materials are ordinarily less soluble and the rate of release of the encased agent is dependent upon the rate of hydration of the engulging matrix. For some applications it is imperative that the ultimate product in which the composition of the invention is incorporated be dissolvable to form a clear solution. Specific encasing agents must be selected to achieve this goal. No single encapsulating material is suitable for all purposes, and in some applications, a combination of two matrix materials, such as proteins and modified starches may be desirable. Since some modified starches contribute flavor to the ultimate products, a gum matrix such a gum acacia may be preferred.
The active agent or agents to be encased in the matrix may be any of many materials including but not limited to flavorings, perfumes, oleoresin, vegetable oils, vitamins, sugar, flavor potentiators, such as acetaldehyde, delicate butter flavors and chemicals such as insecticides. In substance, the encased agent may be any compound which may be rendered more suitable for use or more convenient in a particular system, either by reason of minimizing oxidation, controlling release of the encased material, preventing flavor deterioration on storage, or for any other useful purpose.
In carrying out the process of the invention, the concentration of water relative to the concentration of encasing material is critical, but does not lend itself to precise mathematical definition. The quantity of water should be only sufficient to produce a viscous paste with the encapsulating material so that the active agent can be distributed as a microdispersion throughout the resulting homogenous matrix. Empirically, it has been found that suitable operating viscosities range from about 50,000 to about 1,000,000 centipoises or more. It is required that the product be firm but flowable and that the water be adequate to ensure sufficient hydration of the matrix material to permit the establishment of the microdispersion in a homogeneous encapsulation medium.
The process of the invention embraces a broad temperature range extending from below room temperature to near the boiling temperature of water. To a marked degree, the temperature used is dictated by the physical and chemical properties of the agent to be encased. For example, acetaldehyde is encapsulated at a temperature well below its boiling point of 78.degree. F., butter flavors in the temperature range of about 150.degree. F., and essential oils such as oil of clove at a temperature of about 185.degree. F.
A key and controlling step in the process of the invention relates to "shear". While the precise apparatus to be used in achieving this shearing action is not critical, it has been found that a plow mixer similar to a Littleford is quite efficacious. This machine provides a hurling, whirling action produced by the movement of plow-shaped mixing tools causing intense but controlled intermingling of the component elements of the mix. High speed chopper blades break up any agglomerates. Other suitable equipment includes the Baker Perkins Ko-Kneader blender which provides high shear and high intensity mixing of the viscous mass without development of compression or compaction forces.
A characterizing feature of the processing system of the subject invention is its high viscosity. Using appropriate equipment, such as plow mixers, it is possible, in accordance with the invention, to develop sufficient resistance in the viscous mass so as to effect the required dispersion of the active agent throughout the encapsulating medium. Conventional solutions and low viscosity mixtures or pastes are avoided, as are systems which are adapted for spray drying. The viscous mass produced in accordance with the invention is such that it may promptly be shaped or formed into sheets or rods, on chilled rolls or other suitable equipment.
Not all parameters which control the efficacy of the forming operation are completely know, but it has been established that the product discharged from the agitator must not be too sticky and must have sufficient physical integrity in a relatively thin sheet, rod, or other shape so that it may be conveyed to a suitable dryer while retaining, generally, its shape and form. The encapsulating medium must be homogeneous. This is critical. Control of the moisture content during dispersion formation is very important. Care is taken not to drive off substantial amounts of water during this critical step.
A modified starch (Capsul)* has been found to form an excellent matrix in a system in which about 5 pounds of water is used for each 20 pounds of the Capsul, to encapsulate about 20% by weight of an active agent such as an essential oil. The viscous mass has a viscosity in excess of 1,000,000 centipoises when it leaves the reactor. This product sheets readily and can then be dried without significant loss of the microdispersed active material. If in the same type of system, the water concentration is increased to 25% (based on the total of the modified starch and the water) the resulting product is much more fluid, and it becomes extremely difficult to form the desired sheet using chilled rolls. If the water concentration is increased somewhat more (7 pounds of water to 20 pounds of Capsul), to a concentration of about 26%, upon addition of 20% of active agent (based on the total weight of encasing agent and active agent), the resulting mixture is fluid with a viscosity of about 34,000 centipoises. This too-fluid material could not be effectively formed or shaped into a film or sheet. FNT *National Starch and Chemical Corp.
The optimum concentration of water will, of course, vary with the particular type of encapsulating medium used. For example, for gum acacia, a preferred water concentration is about 37.5% by weight or 11 pounds of water to about 20 pounds of gum acacia. This ratio makes it possible to achieve the required viscosity for effective sheeting. If the water concentration is increased to about 41% (14 pounds of water to 20 pounds of gum acacia), the resulting mixture is a fluid with a viscosity of only about 16,000 centipoises. This product could not be sheeted effectively or formed.
Once the sheet consisting of the homogeneous matrix with the active agent dispersed therethrough as micron particles is formed, it is conveyed through a suitable drying tunnel and pre-dried at a temperature in the range of about 110.degree. F. to about 150.degree. F. with a high velocity air stream so that within about two to ten minutes sufficient moisture has been dispelled to render the sheet somewhat brittle. It is then physically broken into smaller pieces using equipment such as a Comitrol chopper. The smaller pieces can then be dried further, followed by grinding. It has been found advantageous to reduce the size of the sheets when the product itself still contains 10 to 20% moisture. The coarsely ground material is then subjected to final drying and further grinding if desired. In some applications, the predrying step is not necessary. The procedure outlined is effective to minimize fissure points, facilitating the final grinding and producing products with enhanced conversion and stability.
The selected degree of granulation for the finished product is affected by the contemplated end use. For example, if the product is to be incorporated in chewing gum, where grittiness is to be avoided, the final product is finely ground, normally to pass a 100 mesh screen. Conversely, a product to be used in bath salts is ground very coarsely. Since the rate of flavor release is dependent, in part, on the "mesh" of the final product, in some applications the product is ground through a 10 mesh screen, in others a 40 mesh screen, or even finer. An advantage of the invention is its simple flexibility particularly as to the specific size of granules to be achieved in the final preparation. In contrast, the spray drying technique of the prior art provides no corresponding option. The spray dried product is always a very fine powder.
In accordance with the practice of the invention, certain modified starches are suitable as encapsulating agents; others are not.
In spray drying, the ratio of water to the encasing agent is evidently sufficient to render many modified starches suitable as the enveloping film material. In contrast, in the method of the present invention it has been found that the selection of a suitable modified starch is critical since some of these products such as Capsul are suitable while others, for example, Nadex 772, which is also made by National Starch and Chemical Corporation, did not provide a good micro-dispersion, and when the product was sheeted free essential oil was expelled. Free essential oil was also found in the mixer. Yet, this same product is described as excellent for use in the production of spray dried products, and shows good stability against oxidation. An additional modified starch, also found to be excellent in spray drying processes is National 46. Again, this particular modified starch does not function well in the practice of the present invention.
One additional modified starch which has been found to be suitable in the practice of the invention is identified by the brand name Purity Gum BE. The modified starch formed a functional viscous mass when combined with 23% water, and the system provided good encapsulation and products of excellent stability.
The chemistry of modified starches is extremely complex, and much of the pertinent information is maintained as trade secrets. However, it has been possible to relate some of the available information to determine functionality as it relates to the subject invention. Based upon the teachings of the invention as set forth herein, those skilled in the art will be able to determine with a minimum of "experimentation" and with simple tests which modified starches are functional and which are not.
In the efficient and practical practice of the invention, one goal is to convert 90% or more of the essential oil into the finished product. In working with very volatile materials such as acetaldehyde, a conversion of 40% is sought. In the encapsulation of butter flavors, the conversion of materials such as butyric acid and diacetyl is essentially quantitative. Regarding the stability of the ultimate products the goal of the invention is 90% or better.
One prior art process for the production of artificial spice particles is described in Galluzzi et al U.S. Pat. No. 3,922,354. That process is materially different from the process of the present invention, and the products of Galluzzi are readily distinguishable from the products of the instant invention. Galluzzi forms a "difficulty flowable mash" using gelatinized cereal solids as the major component, heats the mass until some gelation takes place, while the water concentration is reduced from about 30% to about 15%, cools, and then adds a flavoring agent to the cooled mass, with agitation. Finally, the Galluzzi product is further cooled to harden, and the hardened mass ground. As expressly taught by Galluzzi and as clearly illustrated in the drawing of the Galluzzi patent, the flavoring agent is "dispersed" in a heterogeneous matrix consisting of 2 components. One is the hardened gelatined material, and the other component consists of physically distinct "chucks" of insoluble farinaceous material constituting the ungelatinized cereal solids. Isolated pockets or globules of the flavoring agent are shown in this heterogeneous matrix.
Galluzzi produces no microdispersion of flavoring agent in the sense of the instant invention. This fact is clear from a consideration of the Galluzzi specification and from the patent drawing, a 120X magnification of Galluzzi's artificial spice particle. The Galluzzi flavoring agent globules are much larger than the micron-submicron particles of the dispersed phase of the subject invention. They do not constitute a microdispersion in a homogeneous matrix.
In fundamental contrast with the method and products of Galluzzi et al, the active agent of the present invention is dispersed as micron size and sub-micron particles throughout a homogeneous matrix. The instant system is a two component system rather than the three component system of Galluzzi et al. Moreover, tests carried out to compare the products produced establish conclusively that the flavor agents of Galluzzi are not encased and protected as they are in the present invention. There is substantial loss of essential oil from the "matrix" upon incubation of the Galluzzi product. After four days at 100.degree. F., essential oil losses ranged from 50% to 83%. For products made in accordance with the present invention, the losses were only 5 to 10%, under the same test conditions. The flavor oil does not act as truly encapsulated in the Galluzzi product. Rather, the oil is an unprotected component of a heterogeneous system.